Photolithographic processes have hitherto been used for manufacturing FPDs such as liquid crystal displays, semiconductor devices, CCDs, color filters and the like. For example, the photolithographic process for producing an integrated circuit device comprises: spreading a positive- or negative-working resist composition on a substrate; removing the solvent of the composition by baking; exposing the resist to radiation such as ultraviolet rays, far ultraviolet rays, electron beams or X-rays; and developing the exposed resist to form a resist pattern.
In many cases, the substrate used in the process has a high reflectance. Accordingly, in the exposure step, light having passed through the resist layer is often reflected by the substrate and then reenters the resist layer again, so that the light is applied to the resist layer even in areas not expected to be exposed. As a result, there is a problem that the aimed pattern cannot be obtained or that the obtained pattern may have defects. Further, reflection of the light at the interface between the substrate and the resist layer often causes a standing-wave effect to corrugate the resist layer, and consequently serious troubles may occur in controlling the line width of the resist pattern. These phenomena are remarkable particularly when light of a shorter wavelength is used in the exposure step to form a finer pattern.
For the purpose of coping with those problems, various methods have been studied and developed. For example, there have been proposed a method in which a dye having absorption in the wavelength range of light for exposure is dispersed in the resist, a method in which a bottom anti-reflection coating (BARC) or a top anti-reflection coating (TARC) is provided, a top surface imaging (TSI) method, and a multilayer resist (MLR) method. Among them, the method employing a bottom anti-reflection coating is most popularly adopted at present. As the bottom anti-reflection coating, there are known inorganic anti-reflection coatings and organic ones. The inorganic coatings can be formed by known methods in which inorganic or metal material is deposited according to, for example, CVD (chemical vapor deposition) process, normal vapor deposition process or sputtering process. The organic coatings can be also formed by known methods in which the substrate is coated, for example, with an organic polymer solution dissolving or dispersing a dye or with a solution or dispersion of a polymer dye containing chromophores chemically combined with a polymer skeleton.
Meanwhile, it is known that a top anti-reflection coating can be formed by applying a composition containing a fluorine compound, such as perfluorooctanic acid or perfluorooctanesulfonic acid, onto the top surface of the resist layer. The top anti-reflection coating reduces interference of light caused by thickness variation of the resist layer, so as to form a pattern in the aimed shape. It is, therefore, required for the top anti-reflection coating to have both a low refractive index and a high transmittance.
It is known that multiple interference changes the pattern dimension to the smallest degree when the refractive index of the top anti-reflection coating (nt) and that of the resist layer (nr) satisfy the condition of: nt=√nr. On the other hand, when the resist layer is treated with an ArF excimer laser, the refractive index of the resist layer is normally approx. 1.70 at 193 nm, which is the wavelength of ArF excimer laser beams. Accordingly, in that case, the optimal refractive index of the top anti-reflection coating is approx. 1.30.
In spite of that, it is difficult to form a top anti-reflection coating having such a low refractive index. In many practical cases, a top anti-reflection coating having a relatively low refractive index is formed from highly fluorinated polymer materials. However, even though the top anti-reflection coating is formed from those materials, its refractive index is nevertheless not less than approx. 1.4. Further, the highly fluorinated polymer materials are generally expensive, and hence it has been desired to replace them with a new composition for forming a top anti-reflection coating.
In the meantime, it is studied to make the anti-reflection coating have absorption at a particular wavelength so as to obtain preferred effects by use of anomalous dispersion (see, Patent document 1). The term “anomalous dispersion” means a phenomenon in which the refractive index changes drastically at the wavelength where the coating absorbs light. However, Patent document 1 is silent about what compound should be used for the coating exposed to light of a short wavelength such as an ArF excimer laser beam. Further, the present inventors' study has revealed that, in order to obtain the preferred refractive index, it is not enough if the absorption wavelength merely corresponds to the exposure wavelength.    [Patent document 1] U.S. Pat. No. 6,274,295